In manufacturing processes there is often a requirement that the workpiece be moved from station to station for successive operations. If the manufacturer wants his process to be automated, he must have some mechanical device to accomplish the transfer. Since manufacturing efficiency demands automation, there are myriad inventions in the prior art tailored to this purpose.
Many of the devices in the prior art are tailored specifically to a given manufacturing process. The "Transporter for Injection-Molded Parts or Inserts Therefor" of Herbert Rees and Klaus B. Fritzsche, U.S. Pat. No. 4,368,018, issued Jan. 11, 1983, is one example. Another is the "Method and Apparatus for Removing and Transferring Finished Glass Articles" of Urban P. Trudeau, U.S. Pat. No. 3,137,394, issued June 16, 1964. Somewhat more general methods of transfer are disclosed in other inventions, as in the "Workpiece Distributors" of Poyet, et al., U.S. Pat. No. 3,215,284, issued Nov. 2, 1965, which discloses a device for distributing workpieces in machining processes. A similar device is the "Automatic Transfer Mechanism for Press Line" of James C. Danly, U.S. Pat. No. 3,199,443, issued Aug. 10, 1965.
The preceding devices all envision usage in a "heavy" industrial setting. As such, design considerations such as contaminant production, high precision of motion reproducibility, and space constraints are not of utmost importance. Therefore, in the "heavy" industrial setting, the large, gear-driven devices are quite satisfactory.
One of the major applications for a transfer device, particularly in the Silicon Valley, is in the semiconductor industry. Given the special environment of semiconductor processing, it is clear that special equipment is required. One prior art device directed to this area is the "Micromanipulator" of Charles Fredrick Miller, U.S. Pat. No. 3,403,575, issued Oct. 1, 1968. Another is the "Object Transport Apparatus" of James D. Ott, U.S. Pat. No. 4,364,707, issued Dec. 21, 1982.
These latter devices reflect the needs of the semiconductor fabrication process. The heavy, contaminant producing oil lubricated gear drives are gone. The Ott device discloses a method of transfer that utilizes an electric stepping motor. Motion is imparted to the workpiece through a belt and pulley combination. The Miller device, although manually powered, reflects the preference for the belt and pulley arrangement in the clean room environment.
Belts and pulleys require no lubrication and are preferable for clean room use in all but the newest plants in that they generate relatively little particulate contamination. The inherent problem is that the belts must stretch and wear, so that the devices' motion reproducibility eventually must be impaired. The same is true even if a gear and sprocket combination is used.
Applicant also notes that various commercially available machines utilize transfer devices whose mechanisms are known to applicant. Among these are the "Wafer Transfer Arm" of SCSS instruments, the "Heatpulse 2101" of A. G. Associates, and the "Microvision 360" of Optical Specialties, Inc. These devices are commonly advertised in the semiconductor trade journals.
A need existed for a transfer device that had a very high degree of motion reproducibility, while still allowing for smooth travel of the parts. Further a need existed for a device that could accomplish the above while taking up very little space and being compatible with a clean room environment.